1. Technical Field
The present invention relates to an apparatus for controlling a permanent-magnet rotary electric machine.
2. Related Art
Permanent-magnet rotary electric machines (e.g., a three-phase direct-current (DC) brushless motor) each having a permanent magnet and an armature in a rotor and a stator, respectively, need to manipulate the phase of a voltage to be applied to the armature (more specifically, a voltage to be applied to the winding of each phase of the armature (hereinafter referred to as an “armature-applied voltage”)) according to the positions (more specifically, the rotation angular positions) of the magnetic poles of the rotor to control the generated torque and the rotational speed thereof. Thus, the permanent-magnet rotary electric machine of such a type has a magnetic pole position detector for detecting the positions of the magnetic poles of the rotor, and manipulates the phase of the armature-applied voltage according to the detected positions of the magnetic poles. The magnetic pole position detector includes a Hall element, an encoder, a resolver, or the like.
In a case where a permanent-magnet rotary electric machine with the above magnetic pole position detector is controlled, an error often occurs between the positions of the magnetic poles detected by the magnetic pole position detector and the actual positions thereof due to the accuracy of positioning of the magnetic pole position detector at the attachment thereof to the machine and that of manufacturing thereof. If such an error occurs, the rotary electric machine has its power factor and efficiency lowered by manipulating the phases of the armature voltages using the detected positions of the magnetic poles as they are.
There has been known a technique of correcting the detected positions of magnetic poles as described in, e.g., JP-A-2001-8486 (Paragraph Nos. 0008, 0018 to 0021). The technique described in JP-A-2001-8486 (Paragraph Nos. 0008, 0018 to 0021) has been developed by focusing attention on the fact that, in a rotary electric machine (cylindrical machine) having a rotor whose magnet is cylindrically shaped, when armature voltages are manipulated to minimize armature currents (phase currents) in a case where a torque T generated by the rotary electric machine is proportional to a q-axis current Iq, and where a load torque is constant, the ratio between a d-axis current command value and the armature current or the ratio between the d-axis current command value and a q-axis current command value has a certain correlation with an error angle between the position of each of the magnetic poles, which is detected by the magnetic pole position detector, and the associated actual position thereof. According to the technique described in JP-A-2001-8486 (Paragraph Nos. 0008, 0018 to 0021), the error angle is calculated based on the value of the above ratio. The detected positions of the magnetic poles are corrected based on the calculated error angle to thereby control the rotary electric machine.
However, according to the technique described in JP-A-2001-8486 (Paragraph Nos. 0008, 0018 to 0021), it is assumed that the torque T generated by the rotary electric machine is proportional to the q-axis current Iq. Thus, the technique described in JP-A-2001-8486 (Paragraph Nos. 0008, 0018 to 0021) cannot be applied to a rotary electric machine (salient-pole machine) having a rotor whose magnets are of the salient pole type. That is, as described in JP-A-2001-8486 (Paragraph Nos. 0008, 0018 to 0021), the torque T generated by a permanent-magnet rotary electric machine is expressed by the following equation (A):T=Φ·Iq+(Ld−Lq)·Id·Iq  (A)Where Φ designates a magnetic flux, Ld, and Lq represent a d-axis inductance and a q-axis inductance, respectively, and Id and Iq denote a d-axis current and a q-axis current, respectively.
In this case, Ld=Lq in a cylindrical machine whose magnet is cylindrically-shaped. Thus, the torque T is proportional to the q-axis current Iq. However, Ld≠Lq in a salient-pole machine whose magnet is of the salient pole type. Thus, the torque T is not proportional to the q-axis current Iq. Consequently, the above prerequisite to the technique described in JP-A-2001-8486 (Paragraph Nos. 0008, 0018 to 0021) is not satisfied by the salient pole machines. Accordingly, the detected positions of the magnetic poles cannot appropriately be corrected.
A technique described in Japanese Patent No. 3,688,673 solves the above problems. FIG. 8 is a block diagram illustrating the internal configuration of a control apparatus for a permanent magnet rotary electric machine whose rotor is connected to an output shaft of an engine, disclosed in Japanese Patent No. 3,688,673. FIG. 9 is a graph illustrating change in each of the number of rotations of the engine, a d-axis current, a q-axis current and a voltage phase, which are measured when the control apparatus illustrated in FIG. 8 obtains a magnetic pole position correction quantity. The voltage phase is equal to an arctangent tan−1 (Vdc/Vqc) of a ratio (Vdc/Vqc) of a d-axis voltage command value Vdc to a q-axis voltage command value Vqc.
In a state in which a rotor 4 of a permanent magnet rotary electric machine 1 is rotated by an engine 3 at a constant number of rotations as illustrated in FIG. 9, and in which an armature current is substantially zero, the control apparatus illustrated in FIG. 8 performs a dq vector control process of handling the rotary electric machine 1 on a dq coordinate system that has a d-axis extending in the direction of a magnetic field of the permanent magnet 5 of the rotor 4 and a q-axis extending in a direction perpendicular to the d-axis. Thus, the control apparatus obtains a magnetic pole position correction quantity for correcting the position of magnetic poles detected by a magnetic pole position detector 8, such that a d-axis voltage command value obtained by performing the dq vector control process is substantially zero. The control apparatus manipulates the phase of an armature voltage using the magnetic pole positions obtained by correcting the detected magnetic pole positions using the magnetic pole position correction quantity.
Hereinafter, the derivation of the magnetic pole position correction quantity based on the technique described in Japanese Patent No. 3,688,673 is described. Referring to FIG. 10A, d-q coordinates represent dq coordinates (hereinafter referred to as actual coordinates d-q) in the case of setting the direction of the actual magnetic field of the rotor 4 along the d-axis. Referring next to FIG. 10B, dc-qc coordinates represent dq coordinates (dq coordinates (hereinafter referred to as “command-axis coordinates dc-qc”) used in the aforementioned dq vector control process) determined by the positions (hereinafter referred to as “detected magnetic pole positions”) of magnetic poles, which are detected by a magnetic pole position detector.
Attention is now focused on a state (hereinafter referred to as a “zero-current state”) in which the rotor 4 of the permanent-magnet rotary electric machine 1 rotates and in which an armature current I (electric current flowing through each phase of the armature) thereof is “0”. In the zero-current state, a voltage V applied to the armature (i.e., a voltage applied to each phase of the armature) is equal to a counter-electromotive voltage E generated by the magnetic field of the rotor 4. In this case, it is assumed that no error occurs between the detected magnetic pole positions and true magnetic pole positions. That is, as illustrated in FIG. 10A, each of actual coordinates d-q coincides with an associated one of command-axis coordinates dc-qc. At that time, a d-axis voltage command value (voltage command value on the command axis dc) Vdc determined by performing the dq vector control process is Vdc=0, and a q-axis voltage command value (voltage command value on the command axis qc) Vqc determined by the dq vector control process is Vqc=E.
Therefore, in a state in which the d-axis voltage command value Vdc determined by the dq vector control process in the zero-current state is “0”, the magnetic pole positions can correctly be detected. This means that it is sufficient for correctly grasping the magnetic pole positions to correct the detected magnetic pole positions so that the d-axis voltage command value Vdc is “0” in the zero-current state.
It is now assumed that an error occurs between the detected magnetic pole positions and true magnetic pole positions. For example, as illustrated in FIG. 10B, the command-axis coordinates dc-qc have an error of an angle θofs (hereinafter, the angle θofs is referred to as a “magnetic pole position error angle θofs”) with respect to the associated actual coordinates d-q. At that time, the d-axis voltage command value Vdc (voltage command value on the command axis dc) determined by performing the dq vector control process is such that Vdc≠0. The q-axis voltage command value Vqc (voltage command value on the command axis qc) is such that Vqc≠E. The square root of the sum (Vdc2+Vqc2) of Vdc2 and Vqc2 is equal to the magnitude of the counter-electromotive voltage E. The ratio (Vdc/Vqc) of the d-axis voltage command value Vdc to the q-axis voltage command value Vqc is equal to the tangent tan θofs of the magnetic pole position error angle θofs. That is, the following equation (1) holds.θofs=tan−1(Vdc/Vqc)  (1)
The magnitude of the counter-electromotive voltage E (thus, the magnitude of each of the d-axis voltage command value Vdc and the q-axis voltage command value Vqc) depends upon the rotational speed of the rotor. The equation (1) holds regardless of the rotational speed of the rotor 4 if the permanent-magnet rotary electric machine is in the zero-current state. The equation (1) is equivalent to the following equation (2) or (3):θofs=sin−1{Vdc/(√{square root over (Vdc2+Vqc2)})}  (2)θofs=cos−1{Vqc/(√{square root over (Vdc2+Vqc2)})}  (3)
Consequently, the magnetic pole position error angle θofs can be determined according to the equation (1) or (2) or (3) from the d-axis voltage command value Vdc and the q-axis voltage command value Vqc that are determined by the dq vector control process in the zero-current state. The correct magnetic pole positions can be grasped by correcting the detected magnetic pole positions by the magnetic pole position error angle θofs thus determined. For example, if the rotational angular position of a magnetic pole corresponding to a detected magnetic pole position is represented by θact, an angle (θact−θofs) obtained by subtracting a magnetic pole position error angle θofs from the angular position θact represents a correct magnetic pole position (true magnetic pole position).
The above principles hold, regardless of whether the magnet of the rotor 4 is of the cylindrical type or the salient-pole type.
According to the technique described in Japanese Patent No. 3,688,673, the magnetic pole position correction quantity θofs is obtained on the basis of a predetermined operation expression (equation (1) or (2) or (3)) from the d-axis voltage command values Vdc and the q-axis voltage command value Vqc obtained by performing the dq vector control process in the zero-current state. Thus, a magnetic pole position that obtained by correcting the detected magnetic pole position using the magnetic pole position correction quantity θofs coincides with an actual magnetic pole position of the rotor 4 regardless of whether the permanent-magnet rotary machine is a cylindrical machine or a salient-pole machine. Accordingly, an operation (torque or speed thereof) of the rotary electric machine 1 can be controlled, without impairing the efficiency and power factor of the rotary electric machine 1, by manipulating the phase of the armature voltage according to the corrected magnetic pole position.
According to the technique described in Japanese Patent No. 3,688,673, even when a command is issued to bring the machine into a state (zero-current state) in which the armature current (i.e., the d-axis current Id and the q-axis current Iq) is substantially zero, as illustrated in FIG. 9, it takes a certain time until a pulse-width modulation (PWM) inverter circuit 17 provided in the control apparatus illustrated in FIG. 8 stably outputs a voltage corresponding to the command. That is, due to the influence of the response of a switching element of the PWM inverter circuit 17, there is a dead time after the issuance of the command until the output of the PWM inverter circuit 17 is stabilized. Accordingly, as illustrated in FIG. 9, the voltage phase is gradually converged. That is, the response speed of the voltage phase at obtaining the magnetic pole position correction quantity θofs is low. However, it is desirable that the response speed is high.
When the response of the voltage command generator is improved, the response time of the voltage phase is reduced. However, the PWM inverter circuit responds to the variation error of the current command. In this case, the stability of an output voltage is reduced. The stability of the voltage phase responding to the current command is degraded.